The present invention relates to a door control device comprising a housing, a slide which is slidable along a path in the housing and a control member mounted for turning relative to the housing about an axis which is transverse to said path, the slide having a row of drive elements which are spaced apart along the path and the control member having a number of drive elements which are arranged around the axis for co-operation with respective ones of the drive elements of the slide to transmit drive between the control member and the slide. In use, the housing is mounted on one of a door and a fixed structure defining a doorway to be closed by the door. The control member is typically connected by means including a radial arm with the other of the door and the fixed structure so that opening of the door causes turning of the control member relative to the housing and therefore displacement of the slide along its path inside the housing. There is provided inside the housing means which co-operates with the slide to control movement thereof and therefore movement of the door relative to the fixed structure. This means typically includes a spring acting between the slide and the housing and a fluid which is caused to flow through one or more orifices when the slide moves along its path in the housing.
In known door control devices of the kind described, the slide is typically formed from a single piece of metal by machining. This is a relatively expensive procedure. In GB No. 2,110,297, we have disclosed a slide which is fabricated from a tube, a pair of end plugs and a rack. The tube is cut from drawn tubular stock and a part of the tube is cut-away to form windows in the tube, through which the control member can extend. The end plugs are machined and then one end plug is inserted into an end portion of the tube. The rack is formed separately, is inserted into the tube and then the other end plug is inserted so that the rack is trapped inside the tube. The end plugs and rack are brazed to the tube. The tube is required to have an external profile which compliments the internal profile of the housing so that the slide will function as a piston in the housing.
The door control device disclosed in GB No. 2,110,297 comprises a coiled compression spring which acts between the slide and the housing. When a door which is controlled by the device is opened, the spring is compressed. The spring subsequently provides energy to close the door. The magnitude of the force exerted by the spring on the slide depends upon the degree of compression of the spring and falls, as the spring extends. In order to ensure that, just as the door closes and a latch associated with the door must be overcome, the spring exerts sufficient force, it is necessary for the spring to exert an excessively large force when the door is opened wide.